critical

    4.0.1 • Public • Published

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    critical

    Critical extracts & inlines critical-path (above-the-fold) CSS from HTML

    Preview

    Install

    npm i -D critical

    Build plugins

    Demo projects

    Usage

    Include:

    const critical = require('critical');

    Full blown example with available options:

    critical.generate({
      // Inline the generated critical-path CSS
      // - true generates HTML
      // - false generates CSS
      inline: true,
    
      // Your base directory
      base: 'dist/',
    
      // HTML source
      html: '<html>...</html>',
    
      // HTML source file
      src: 'index.html',
    
      // Your CSS Files (optional)
      css: ['dist/styles/main.css'],
    
      // Viewport width
      width: 1300,
    
      // Viewport height
      height: 900,
    
      // Output results to file
      target: {
        css: 'critical.css',
        html: 'index-critical.html',
        uncritical: 'uncritical.css',
      },
    
      // Extract inlined styles from referenced stylesheets
      extract: true,
    
      // ignore CSS rules
      ignore: {
        atrule: ['@font-face'],
        rule: [/some-regexp/],
        decl: (node, value) => /big-image\.png/.test(value),
      },
    });

    Generate and inline critical-path CSS

    Basic usage:

    critical.generate({
      inline: true,
      base: 'test/',
      src: 'index.html',
      target: 'index-critical.html',
      width: 1300,
      height: 900,
    });

    Generate critical-path CSS

    Basic usage:

    critical.generate({
      base: 'test/',
      src: 'index.html',
      target: 'styles/main.css',
      width: 1300,
      height: 900,
    });

    Generate and minify critical-path CSS:

    critical.generate({
      base: 'test/',
      src: 'index.html',
      target: 'styles/styles.min.css',
      width: 1300,
      height: 900,
    });

    Generate, minify and inline critical-path CSS:

    critical.generate({
      inline: true,
      base: 'test/',
      src: 'index.html',
      target: {
        html: 'index-critical.html',
        css: 'critical.css',
      },
      width: 1300,
      height: 900,
    });

    Generate and return output via callback:

    critical.generate({
        base: 'test/',
        src: 'index.html',
        width: 1300,
        height: 900,
        inline: true
    }, (err, ({css, html, uncritical})) => {
        // You now have critical-path CSS as well as the modified HTML.
        // Works with and without target specified.
        ...
    });

    Generate and return output via promise:

    critical.generate({
        base: 'test/',
        src: 'index.html',
        width: 1300,
        height: 900
    }).then((({css, html, uncritical})) => {
        // You now have critical-path CSS as well as the modified HTML.
        // Works with and without target specified.
        ...
    }).error(err => {
        ...
    });

    Generate and return output via async function:

    const {css, html, uncritical} = await critical.generate({
      base: 'test/',
      src: 'index.html',
      width: 1300,
      height: 900,
    });

    Generate critical-path CSS with multiple resolutions

    When your site is adaptive and you want to deliver critical CSS for multiple screen resolutions this is a useful option. note: (your final output will be minified as to eliminate duplicate rule inclusion)

    critical.generate({
      base: 'test/',
      src: 'index.html',
      target: {
        css: 'styles/main.css',
      },
      dimensions: [
        {
          height: 200,
          width: 500,
        },
        {
          height: 900,
          width: 1200,
        },
      ],
    });

    Generate critical-path CSS and ignore specific selectors

    This is a useful option when you e.g. want to defer loading of webfonts or background images.

    critical.generate({
      base: 'test/',
      src: 'index.html',
      target: {
        css: 'styles/main.css',
      },
      ignore: {
        atrule: ['@font-face'],
        decl: (node, value) => /url\(/.test(value),
      },
    });

    Generate critical-path CSS and specify asset rebase behaviour

    critical.generate({
      base: 'test/',
      src: 'index.html',
      target: {
        css: 'styles/main.css',
      },
      rebase: {
        from: '/styles/main.css',
        to: '/folder/subfolder/index.html',
      },
    });
    critical.generate({
      base: 'test/',
      src: 'index.html',
      target: {
        css: 'styles/main.css',
      },
      rebase: asset => `https://my-cdn.com${asset.absolutePath}`,
    });

    Options

    Name Type Default Description
    inline boolean|object false Inline critical-path CSS using filamentgroup's loadCSS. Pass an object to configure inline-critical
    base string path.dirname(src) or process.cwd() Base directory in which the source and destination are to be written
    html string HTML source to be operated against. This option takes precedence over the src option.
    css array [] An array of paths to css files, file globs or Vinyl file objects.
    src string Location of the HTML source to be operated against
    target string or object Location of where to save the output of an operation. Use an object with 'html' and 'css' props if you want to store both
    width integer 1300 Width of the target viewport
    height integer 900 Height of the target viewport
    dimensions array [] An array of objects containing height and width. Takes precedence over width and height if set
    extract boolean false Remove the inlined styles from any stylesheets referenced in the HTML. It generates new references based on extracted content so it's safe to use for multiple HTML files referencing the same stylesheet. Use with caution. Removing the critical CSS per page results in a unique async loaded CSS file for every page. Meaning you can't rely on cache across multiple pages
    inlineImages boolean false Inline images
    assetPaths array [] List of directories/urls where the inliner should start looking for assets
    maxImageFileSize integer 10240 Sets a max file size (in bytes) for base64 inlined images
    rebase object or function undefined Critical tries it's best to rebase the asset paths relative to the document. If this doesn't work as expected you can always use this option to control the rebase paths. See postcss-url for details. (https://github.com/pocketjoso/penthouse#usage-1).
    ignore array object undefined
    userAgent string '' User agent to use when fetching a remote src
    penthouse object {} Configuration options for penthouse.
    request object {} Configuration options for got.
    user string undefined RFC2617 basic authorization: user
    pass string undefined RFC2617 basic authorization: pass
    strict boolean false Throw an error if no css is found

    CLI

    npm install -g critical

    critical works well with standard input.

    cat test/fixture/index.html | critical --base test/fixture --inline > index.critical.html

    Or on Windows:

    type test\fixture\index.html | critical --base test/fixture --inline > index.critical.html

    You can also pass in the critical CSS file as an option.

    critical test/fixture/index.html --base test/fixture > critical.css

    Gulp

    const gulp = require('gulp');
    const log = require('fancy-log');
    const critical = require('critical').stream;
    
    // Generate & Inline Critical-path CSS
    gulp.task('critical', () => {
      return gulp
        .src('dist/*.html')
        .pipe(
          critical({
            base: 'dist/',
            inline: true,
            css: ['dist/styles/components.css', 'dist/styles/main.css'],
          })
        )
        .on('error', err => {
          log.error(err.message);
        })
        .pipe(gulp.dest('dist'));
    });

    Why?

    Why is critical-path CSS important?

    CSS is required to construct the render tree for your pages and JavaScript will often block on CSS during initial construction of the page. You should ensure that any non-essential CSS is marked as non-critical (e.g. print and other media queries), and that the amount of critical CSS and the time to deliver it is as small as possible.

    Why should critical-path CSS be inlined?

    For best performance, you may want to consider inlining the critical CSS directly into the HTML document. This eliminates additional roundtrips in the critical path and if done correctly can be used to deliver a “one roundtrip” critical path length where only the HTML is a blocking resource.

    FAQ

    Are there any sample projects available using Critical?

    Why, yes!. Take a look at this Gulp project which demonstrates using Critical to generate and inline critical-path CSS. It also includes a mini-tutorial that walks through how to use it in a simple webapp.

    When should I just use Penthouse directly?

    The main differences between Critical and Penthouse, a module we use, are:

    • Critical will automatically extract stylesheets from your HTML from which to generate critical-path CSS from, whilst other modules generally require you to specify this upfront.
    • Critical provides methods for inlining critical-path CSS (a common logical next-step once your CSS is generated)
    • Since we tackle both generation and inlining, we're able to abstract away some of the ugly boilerplate otherwise involved in tackling these problems separately.

    That said, if your site or app has a large number of styles or styles which are being dynamically injected into the DOM (sometimes common in Angular apps) I recommend using Penthouse directly. It will require you to supply styles upfront, but this may provide a higher level of accuracy if you find Critical isn't serving your needs.

    What other alternatives to Critical are available?

    FilamentGroup maintain a criticalCSS node module, which similar to Penthouse will find and output the critical-path CSS for your pages. The PageSpeed Optimization modules for nginx, apache, IIS, ATS, and Open Lightspeed can do all the heavy lifting automatically when you enable the prioritize_critical_css filter

    Is Critical stable and suitable for production use?

    Critical has been used on a number of production sites that have found it stable for everyday use. That said, we welcome you to try it out on your project and report bugs if you find them.

    Can I contribute?

    Of course. We appreciate all of our contributors and welcome contributions to improve the project further. If you're uncertain whether an addition should be made, feel free to open up an issue and we can discuss it.

    Maintainers

    This module is brought to you and maintained by the following people:

    License

    Apache-2.0 © Addy Osmani, Ben Zörb

    Install

    npm i critical

    DownloadsWeekly Downloads

    22,953

    Version

    4.0.1

    License

    Apache-2.0

    Unpacked Size

    98.3 kB

    Total Files

    11

    Last publish

    Collaborators

    • bezoerb
    • sindresorhus
    • addyosmani